Stabilization of kerogen thermal maturation: Evidence from geothermometry and burial history reconstruction, Niobrara Limestone, Berthoud oil field, western Denver Basin, Colorado

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6762468

Barker, C E; Crysdale, B L ^[1]

---

1. Geological Survey, Denver, CO (USA)

The burial history of this fractured Niobrara Limestone reservoir and source rock offers a setting for studying the stabilization of thermal maturity because soon after peak temperature of approximately 100{degree}C was reached, exhumation lowered temperature to about 60-70{degree}C. Vitrinite reflectance (Rm = 0.6-0.7%) and published clay mineralogy data from the Niobrara Limestone indicate that peak paleotemperature was approximately 100{degree}C. Fluid inclusion data also indicate oil migration occurred at 100{degree}C. Burial history reconstruction indicates 100{degree}C was reached in the Niobrara Limestone only during minimum burial, which occurred at 70 Ma and 8000 ft depth. However, erosion beginning at 70 Ma and continuing until 50 Ma removed over 3,000 ft of rock. This depth of erosion agrees with an Rm of 0.4% measured in surface samples of the Pierre Shale. The exhumation of the reservoir decreased temperature by about 30{degree}C to near the corrected bottom-hole temperature of 50-70{degree}C. Lopatin time-temperature index (TTI) analysis suggests the Niobrara Limestone as a source rock matured to the oil generation stage (TTI = 10) about 25 Ma, significantly later than maximum burial, and after exhumation caused cooling. The Lopatin TTI method in this case seems to overestimate the influence of heating time. If time is an important factor, thermal maturity should continue to increase after peak burial and temperature so that vitrinite reflectance will not be comparable to peak paleotemperatures estimated from geothermometers set at near-peak temperature and those estimated from burial history reconstruction. The agreement between geothermometry and the burial history reconstruction in Berthoud State 4 suggests that the influence of heating time must be small. The elapsed time available at near peak temperatures was sufficient to allow stabilization of thermal maturation in this case.

• OSTI ID: 6762468
• Report Number(s): CONF-900605--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
CARBONATE ROCKS
COLORADO
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOTHERMOMETRY
KEROGEN
LIMESTONE
MACERALS
MATERIALS
MATURATION
MINERAL RESOURCES
NORTH AMERICA
OIL FIELDS
ORGANIC MATTER
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SOURCE ROCKS
USA
VITRINITE